Editing Chess opening (section)

==Classification of chess openings==
{{For|a list of openings as classified by the [[Encyclopaedia of Chess Openings]]|List of chess openings}}

Chess openings are primarily categorized by move sequences.<ref>This is in contrast to [[shogi opening]] theory, which generally categorizes openings by form regardless of the move sequences that brought about the form in what are sometimes called ''systems'' in western chess.</ref> In the initial position, White has twenty legal moves.<ref name="whyldweekend">{{cite book |last=Whyld |first=Kenneth |author-link=Ken Whyld |title=Learn Chess in a Weekend |year=1993 |publisher=Knopf/DK |page=58 |isbn=9780679422297}}</ref> Of these, 1.e4, 1.d4, 1.Nf3, and 1.c4 are by far the most popular as these moves do the most to promote rapid development and control of the center. A few other opening moves are considered reasonable but less consistent with opening principles than the four most popular moves. The [[Dunst Opening]], 1.Nc3, develops a knight to a good square, but is somewhat inflexible because it blocks White's c-pawn; also, after 1...d5 the knight is liable to be driven to an inferior square by ...d4. (Note that after 1.Nf3 the analogous 1...e5{{chesspunc|?}} loses a pawn.) [[Bird's Opening]], 1.f4, addresses center control but not development and weakens the king position slightly. The [[Sokolsky Opening]] 1.b4 and the King's and Queen's [[fianchetto]]s: [[Larsen's Opening]] 1.b3 and 1.g3 aid development a bit, but they only address center control peripherally and are slower than the more popular openings. The eleven remaining possibilities are rarely played at the top levels of chess. Of these, the best are merely slow such as 1.c3, 1.d3, and 1.e3. Worse possibilities either ignore the center and development such as 1.a3, weaken White's position (for instance, 1.f3 and 1.g4), or place the knights on poor squares (1.Na3 and 1.Nh3).

Black has twenty complementary responses to White's opening move.<ref name="whyldweekend" />  Many of these are mirror images of the most popular first moves for White, but with one less [[tempo (chess)|tempo]]. Defenses beginning with 1...c6 and 1...e6, often followed by the center thrust 2...d5, are also popular. Defenses with an early ...d6 coupled with a [[kingside]] [[fianchetto]] are also commonly played.

The most important scheme of classifying chess openings for serious players is by [[list of chess openings|''ECO'' code]], a series of 500 opening codes assigned by the ''[[Encyclopaedia of Chess Openings]]''. Although these codes are invaluable for the serious study of the chess opening, they are not very practical for a broad survey of the chess opening as the codes obscure common structural features between related openings.

A simple descriptive categorization of the chess opening is [[King's Pawn Game|king's pawn openings]], [[Queen's Pawn Game|queen's pawn openings]], and others. Since these categories are still individually very large, it is common to divide each of them further. One reasonable way to group the openings is:
* Double king pawn, symmetric or [[open game]]s (1.e4 e5)<ref>Chess Openings for White Explained, p. 27, {{ISBN|1-889323-11-X}}</ref>
* Single king pawn or [[semi-open game]]s (1.e4 other)
* Double queen pawn or [[closed game]]s (1.d4 d5)
* Single queen pawn or [[semi-closed game]]s (1.d4 other)
* [[Flank opening]]s (including 1.c4, 1.Nf3, 1.f4, and others)
* [[irregular chess opening|Unusual first moves]] for White
The [[Indian defence|Indian systems]] (1.d4 Nf6) are the most important<ref>Chess Opening Essentials 3, p. 38, {{ISBN|978-90-5691-308-3}}</ref> of the semi-closed games, and warrant separate treatment.

===Open games: 1.e4 e5===
{{Main article|Open Game}}
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White starts by playing 1.e4 (moving their king pawn two spaces). This is the most popular opening move and it has many strengths—it immediately works on controlling the center, and it activates two pieces (the queen and a bishop). The oldest openings in chess follow 1.e4. [[Bobby Fischer]] rated 1.e4 as "Best by test." On the downside, 1.e4 places a pawn on an undefended square and weakens d4 and f4. If Black mirrors White's move and replies with 1...e5, the result is an open game.

The most popular second move for White is 2.Nf3 attacking Black's king pawn, preparing for a kingside castle, and anticipating the advance of the queen pawn to d4. Black's most common reply is 2...Nc6, which usually leads to the [[Ruy Lopez]] (3.Bb5), [[Scotch Game]] (3.d4), or [[Italian Game]] (3.Bc4). If Black instead maintains symmetry and counterattacks White's center with 2...Nf6 then the [[Petrov's Defense]] results. The [[Philidor Defense]] (2...d6) is not popular in modern chess because it allows White an easy space advantage while Black's position remains cramped and passive, although solid. Other responses to 2.Nf3 are not seen in master play.

The most popular alternatives to 2.Nf3 are the [[Vienna Game]] (2.Nc3), the [[Bishop's Opening]] (2.Bc4), and the [[King's Gambit]] (2.f4). These openings have some similarities with each other, in particular the Bishop's Opening frequently transposes to variations of the Vienna Game. The King's Gambit was extremely popular in the 19th century. White sacrifices a pawn for quick development and to divert a black pawn from the center. The Vienna Game also frequently features attacks on the Black center by means of a f2–f4 pawn advance.

In the [[Center Game]] (2.d4) White immediately opens the center but if the pawn is to be recovered after 2...exd4, White must contend with a slightly premature queen development after 3.Qxd4. An alternative is to sacrifice one or two pawns, for example in the [[Danish Gambit]].

Many other variations after 1.e4 e5 have been studied; see [[Open Game]] for details.
* 1.e4 e5 Double King's Pawn Opening or [[Open Game]]
* 1.e4 e5 2.Nf3 Nc6 3.Bb5 [[Ruy Lopez]]
* 1.e4 e5 2.Nf3 Nc6 3.d4 [[Scotch Game]]
* 1.e4 e5 2.Nf3 Nc6 3.Bc4 [[Italian Game]]
* 1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6 [[Four Knights Game]]
* 1.e4 e5 2.Nf3 Nf6 [[Petrov's Defense]]
* 1.e4 e5 2.Nf3 d6 [[Philidor Defense]]
* 1.e4 e5 2.Nc3 [[Vienna Game]]
* 1.e4 e5 2.Bc4 [[Bishop's Opening]]
* 1.e4 e5 2.f4 [[King's Gambit]]
* 1.e4 e5 2.d4 exd4 3.Qxd4 [[Center Game]]
* 1.e4 e5 2.d4 exd4 3.c3 [[Danish Gambit]]

===Semi-open games: 1.e4, Black plays other than 1...e5===
{{Main article|Semi-Open Game}}
In the semi-open games White plays 1.e4 and Black breaks symmetry immediately by replying with a move other than 1...e5. The most popular Black defense to 1.e4 is the [[Sicilian Defence|Sicilian]] (1...c5), but the [[French Defence|French]] (1...e6, normally followed by 2.d4 d5) and the [[Caro–Kann Defence|Caro–Kann]] (1...c6, normally followed by 2.d4 d5) are also very popular. The [[Pirc Defense|Pirc]] and the [[Modern Defense|Modern]] are closely related openings that are also often seen, while the [[Alekhine's Defence|Alekhine]] and the [[Scandinavian Defense|Scandinavian]] have made occasional appearances in [[World Chess Championship]] games.

The Sicilian and French Defenses lead to unbalanced positions that can offer exciting play with both sides having chances to win. The Caro–Kann Defense is solid as Black intends to use their c-pawn to support their center (1.e4 c6 2.d4 d5). Alekhine's, the Pirc and the Modern are [[hypermodernism (chess)|hypermodern]] openings in which Black tempts White to build a large center with the goal of attacking it with pieces.

Other semi-open games have been studied but are less common; see [[Semi-Open Game]] for details.
* 1.e4 c5 [[Sicilian Defense]]
* 1.e4 e6 [[French Defense]]
* 1.e4 c6 [[Caro–Kann Defense]]
* 1.e4 d5 [[Scandinavian Defense]] (also known as the Center Counter defense)
* 1.e4 d6 2.d4 Nf6 3.Nc3 g6 [[Pirc Defense]]
* 1.e4 Nf6 [[Alekhine's Defense]]
* 1.e4 g6 [[Modern Defense]]

===Closed games: 1.d4 d5===
{{Main article|Closed Game}}
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The openings classified as closed games begin 1.d4 d5. The move 1.d4 offers the same benefits to development and center control as does 1.e4, but unlike with King Pawn openings where the e4-pawn is undefended after the first move, the d4-pawn is protected by White's queen. This slight difference has a tremendous effect on the opening. For instance, whereas the [[King's Gambit]] is rarely played today at the highest levels of chess, the [[Queen's Gambit]] remains a popular weapon at all levels of play. Also, compared with the King Pawn openings, transpositions among variations are more common and critical in the closed games.

The most important closed openings are in the Queen's Gambit family (White plays 2.c4). The Queen's Gambit is somewhat misnamed, since White can always regain the offered pawn if desired. In the [[Queen's Gambit Accepted]], Black plays ...dxc4, giving up the center for free development and the chance to try to give White an isolated queen pawn with a subsequent ...c5 and ...cxd4. White will get active pieces and possibilities for the attack. Black has two popular ways to decline the pawn, the [[Slav Defense|Slav]] (2...c6) and the [[Queen's Gambit Declined]] (2...e6). Both of these moves lead to an immense forest of variations that can require a great deal of opening study to play well. Among the many possibilities in the Queen's Gambit Declined are the Orthodox Defense, Lasker's Defense, the [[Cambridge Springs Defense]], the Tartakower Variation, and the Tarrasch and Semi-Tarrasch Defenses. Black replies to the Queen's Gambit other than 2...dxc4, 2...c6, and 2...e6 are uncommon.

The [[Colle System]] and [[Stonewall Attack]] are classified as [[queen's pawn game]]s because White plays d4 but not c4. They are also examples of ''Systems'', rather than specific opening variations. White develops aiming for a particular formation without great concern over how Black chooses to defend. Both systems are popular with club players because they are easy to learn, but are rarely used by professionals because a well-prepared opponent playing Black can equalize fairly easily. The Stonewall is characterized by the White pawn formation on c3, d4, e3, and f4, and can be achieved by several move orders and against many different Black setups. The diagram positions and the move sequences given below are typical.

Other closed openings have been studied but are less common; see [[Closed Game]] for details.
* 1.d4 d5 Double Queen's Pawn Opening or [[Closed Game]]
* 1.d4 d5 2.c4 [[Queen's Gambit]]
* 1.d4 d5 2.c4 dxc4 [[Queen's Gambit Accepted]] (QGA)
* 1.d4 d5 2.c4 e6 [[Queen's Gambit Declined]] (QGD)
* 1.d4 d5 2.c4 c6 [[Slav Defense]]
* 1.d4 d5 2.e3 Nf6 3.Bd3 c5 4.c3 Nc6 5.f4 (a typical move sequence) [[Stonewall Attack]]
* 1.d4 d5 2.Nf3 Nf6 3.e3 [[Colle System]]

===Indian defenses: 1.d4 Nf6===
{{Main article|Indian Defence|l1=Indian Defense}}
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The Indian systems are asymmetrical defenses to 1.d4 that employ hypermodern chess strategy. Fianchettos are common in many of these openings. As with the closed games, [[transposition (chess)|transpositions]] are important and many of the Indian defenses can be reached by several different move orders. Although Indian defenses were championed in the 1920s by players in the hypermodern school, they were not fully accepted until Soviet players showed in the late 1940s that these systems are sound for Black. Since then, Indian defenses have been the most popular Black replies to 1.d4 because they offer an unbalanced game with chances for both sides. The usual White second move is 2.c4, grabbing a larger share of the center and allowing the move Nc3, to prepare for moving the e-pawn to e4 without blocking the c-pawn. Black's most popular replies are:
* 2...e6, freeing the king's bishop and leading into the Nimzo-Indian Defense, Queen's Indian Defense, Bogo-Indian Defense, Modern Benoni, or regular lines of the [[Queen's Gambit Declined]],
* 2...g6, preparing a fianchetto of the king's bishop and entering the King's Indian Defense or Grünfeld Defense, and
* 2...c5 3.d5 e6, the Modern Benoni, with an immediate counterpunch in the center.

Advocated by [[Aron Nimzowitsch|Nimzowitsch]] as early as 1913, the [[Nimzo-Indian Defense]] was the first of the Indian systems to gain full acceptance. It remains one of the most popular and well-respected defenses to 1.d4 and White often adopts move orders designed to avoid it. Black attacks the center with pieces and is prepared to trade a bishop for a knight to weaken White's queenside with [[doubled pawns]].

The [[King's Indian Defense]] is aggressive, somewhat risky, and generally indicates that Black will not be satisfied with a draw. Although it was played occasionally as early as the late 19th century, the King's Indian was considered inferior until the 1940s, when it was taken up by [[David Bronstein|Bronstein]], [[Isaac Boleslavsky|Boleslavsky]], and [[Samuel Reshevsky|Reshevsky]]. Despite being [[Bobby Fischer|Fischer]]'s favored defense to 1.d4, its popularity faded in the mid-1970s. [[Garry Kasparov|Kasparov]]'s successes with the defense restored the King's Indian to prominence in the 1980s.

[[Ernst Grünfeld]] debuted the [[Grünfeld Defense]] in 1922. Distinguished by the move 3...d5, Grünfeld intended it as an improvement to the King's Indian which was not considered entirely satisfactory at that time. The Grünfeld has been adopted by World Champions [[Vasily Smyslov|Smyslov]], Fischer, and Kasparov.

The [[Queen's Indian Defense]] is considered solid, safe, and perhaps somewhat [[draw (chess)|drawish]]. Black often chooses the Queen's Indian when White avoids the Nimzo-Indian by playing 3.Nf3 instead of 3.Nc3. Black constructs a sound position that makes no positional concessions, although sometimes it is difficult for Black to obtain good winning chances. [[Anatoly Karpov|Karpov]] was a leading expert in this opening.

The [[Modern Benoni]] is a risky attempt by Black to unbalance the position and gain active piece play at the cost of allowing White a pawn wedge at d5 and a central majority. [[Mikhail Tal|Tal]] popularized the defense in the 1960s by winning several brilliant games with it, and Fischer occasionally adopted it, with good results, including [[World Chess Championship 1972#Game 3|a win]] in his [[World Chess Championship 1972|1972 world championship]] match against [[Boris Spassky]]. Often Black adopts a slightly different move order, playing 2...e6 before 3...c5 in order to avoid the sharpest lines for White.

The [[Benko Gambit]] is often played by strong players, and is very popular at lower levels. Black plays to open lines on the queenside where White will be subject to considerable pressure. If White accepts the gambit, Black's compensation is positional rather than tactical, and their initiative can last even after many piece exchanges and well into the [[Chess endgame|endgame]]. White often chooses instead either to decline the gambit pawn or return it.

The [[Catalan Opening]] is characterized by White forming a pawn center at d4 and c4 and fianchettoing their king's bishop. It resembles a combination of the [[Queen's Gambit]] and [[Réti Opening]]. Since the Catalan can be reached from many different move orders, (one [[Queen's Gambit Declined]]-like move sequence is 1.d4 d5 2.c4 e6 3.Nf3 Nf6 4.g3), it is sometimes called the Catalan System.

The most important Indian Defenses are listed below, but many others have been studied and played; see [[Indian Defense]] for details.
* 1.d4 Nf6 2.c4 c5 3.d5 e6 [[Modern Benoni]]
* 1.d4 Nf6 2.c4 c5 3.d5 b5 [[Benko Gambit]] (or Volga Gambit)
* 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 [[Nimzo-Indian Defense]]
* 1.d4 Nf6 2.c4 e6 3.Nf3 b6 [[Queen's Indian Defense]]
* 1.d4 Nf6 2.c4 e6 3.g3 [[Catalan Opening]]
* 1.d4 Nf6 2.c4 g6 3.Nc3 d5 [[Grünfeld Defense]]
* 1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 [[King's Indian Defense]] (KID)

===Other Black responses to 1.d4===
{{Main article|Semi-Closed Game}}
Of the defenses to 1.d4 other than 1...d5 and 1...Nf6, the most important are the [[Dutch Defense]] and the [[Benoni Defense]].
The Dutch, an aggressive defense adopted for a time by World Champions [[Alexander Alekhine|Alekhine]] and [[Mikhail Botvinnik|Botvinnik]], and played by both Botvinnik and challenger [[David Bronstein]] in their 1951 [[World Chess Championship|world championship match]], is still played occasionally at the top level by [[Nigel Short|Short]] and others. Another fairly common opening is the [[Benoni Defense]], which may become very wild if it develops into the [[Modern Benoni]], though other variations are more solid.

Several other uncommon semi-closed openings have been named and studied, see [[Semi-Closed Game]] for details.
* 1.d4 c5 [[Benoni Defense]]
* 1.d4 f5 [[Dutch Defense]]

===Flank openings (including English, Réti, Bird's, and White fianchettos)===
{{Main article|Flank opening}}
The flank openings are the group of White openings typified by play on one or both flanks.
White plays in [[hypermodernism (chess)|hypermodern]] style, attacking the center from the flanks with pieces rather than occupying it with pawns. These openings are played often, and 1.Nf3 and 1.c4 trail only 1.e4 and 1.d4 in popularity as opening moves.

If White opens with 1.Nf3, the game often becomes one of the d4 openings (closed games or semi-closed games) by a different move order (called ''[[transposition (chess)|transposition]]''), but unique openings such as the [[Réti Opening|Réti]] and [[King's Indian Attack]] are also common. The Réti itself is characterized by White playing 1.Nf3, [[fianchetto]]ing one or both bishops, and not playing an early d4 (which would generally transpose into one of the 1.d4 openings).

The [[King's Indian Attack]] (KIA) is a system of development that White may use in reply to almost any Black opening moves. The characteristic KIA setup is 1.Nf3, 2.g3, 3.Bg2, 4.0-0, 5.d3, 6.Nbd2, and 7.e4, although these moves may be played in several different orders. In fact, the KIA is often reached after 1.e4 when White uses it to respond to a Black attempt to play one of the semi-open games such as the Caro–Kann, French, or Sicilian, or even the open games that usually follow 1.e4 e5. Its greatest appeal may be that by adopting a set pattern of development, White can avoid the large amount of opening study required to prepare to meet the many different possible Black replies to 1.e4.<ref>[[Larry Evans (chess grandmaster)|Larry Evans]] wrote of the King's Indian Attack, "White's resilient setup is truly magical. It throws both players on their own resources and eliminates the need of memorizing long-winded columns of analysis." Larry Evans, ''The Chess Opening for You'', R.H.M. Press, 1975, p. 38. {{ISBN|0-89058-020-0}}.</ref>

The [[English Opening]] (1.c4) also frequently transposes into a d4 opening, but it can take on independent character as well including the Symmetrical Variation (1.c4 c5) and the Reversed Sicilian (1.c4 e5).

[[King's Fianchetto Opening|1.g3]], the King's Fianchetto Opening or Benko's Opening, received renewed attention after [[Pal Benko]] used it to defeat both [[Bobby Fischer|Fischer]] and [[Mikhail Tal|Tal]] in the 1962 [[Candidates Tournament]] in [[Curaçao]]. It is flexible and usually transposes into a known opening such as the King's Indian Attack or Reti Opening.

[[Larsen's Opening]] (1.b3) and the [[Sokolsky Opening]] (1.b4) are occasionally seen in grandmaster play.

With [[Bird's Opening]] (1.f4) White tries to get a strong grip on the e5-square.
The opening can resemble a Dutch Defense in reverse after 1.f4 d5, or Black may try to disrupt White by playing 1...e5{{chesspunc|!?}} ([[From's Gambit]]).
* 1.b3 [[Larsen's Opening]]
* 1.b4 [[Sokolsky Opening]]
* 1.c4 [[English Opening]]
* 1.Nf3 [[Zukertort Opening]] (characteristically followed by fianchettoing one or both bishops, and without an early d4)
* 1.Nf3, 2.g3, 3.Bg2, 4.0-0, 5.d3, 6.Nbd2, 7.e4 [[King's Indian Attack]] (KIA) (moves may be played in many different orders)
* 1.f4 [[Bird's Opening]]
* 1.g3 [[Benko Opening]]
* 1.g4 [[Grob's Attack]]

===Unusual first moves for White===
{{Main article|Irregular chess opening}}
First moves other than the king pawn (1.e4), queen pawn (1.d4), or flank openings (1.b3, 1.b4, 1.c4, 1.Nf3, 1.f4, or 1.g3) are not regarded as effective ways to exploit White's first-move advantage and thus are rarely played. Although some of these openings are not actually bad for White, each of the twelve remaining possible first moves suffers one or more of the following defects compared to the more popular choices:
* too passive for White (1.d3, 1.e3, 1.c3, or 1.Nc3)
* gratuitously weakens White's position (1.f3 or 1.g4)
* does little to aid White's development or control the center (1.a3, 1.a4, 1.h3, or 1.h4)
* develops a [[knight (chess)|knight]] to an inferior square (1.Na3 or 1.Nh3)